A rather thorough presentation of one year’s worth of work on spotted wing drosophila was made at the big entomology meeting on September 13. As this presentation will not be posted anywhere, the following will be a summary of the work and what we know so far, along with some pointers that may be useful for growers to follow in their efforts to control this pest.

Along with various private industry efforts, the work that is being done right now by UC Davis and UCCE on spotted wing drosophila is important.  The California caneberry industry is 56% of the national fresh market production and has a production cycle on the Central Coast starting in April and continuing on until December, creating a situation of considerable potential of economic harm for this pernicious pest.

The trapping portion of this study tested two common bait formulations, yeast + sugar + water and apple cider vinegar, against a water control from late October 2010 to early September 2011.  We are still in the first year of the study so it is a bit early to draw conclusions, but over time the yeast + sugar + water perhaps performed a little better than the apple cider vinegar. Both baits tended to follow the same pattern meaning there was a period of no response to the traps (they caught very few adult flies) from late February to late May and a large increase of adult flies in the late season.  Additionally, there tended to be more females trapped than males. Whether this is a function of there simply being more females in the field than males or that the traps are simply more attractive to females remains something to be investigated.

Sampling for larvae which began mid-May of this year seems to indicate the first generation of larvae may appear before any noticeable adult fly population, and this continues later on through the season as larval peaks correlate with adult population peaks.  Larval and adult fly populations peak after the end of harvest, which only underlines that growers remove the crop as soon as possible after the cessation of fruit production.

A remaining target for us is the whereabouts of the population of spotted wing drosophila during the period of no response to traps (late February to late May).  We are not trapping flies in the fields, but obviously they start to come from somewhere when the season gets underway again in the spring.  We must understand what is going on here, as these stages of low pest activity tend to historically be the areas where the strongest measures of integrated pest management can be applied.

On occasion, we do run across ideas on how to improve our current efforts in developing a decent control regime for the spotted wing drosophila.

The use of sake ("rice wine", correctly pronounced as sa-KKE, not saki) as a trapping medium is one of those ideas.  Initially mentioned in the groundbreaking Kanazawa paper from the 1930's, it was also the subject recently of a short program on NHK (Japan Broadcasting Corporation) on managing vinegar and other flies in the household.
With the generosity of Patrick Kingston, replications of this sake trap (200 ml vinegar, 100 ml sake, 3.5 oz sugar and dubbed the "sake bomb")  were tested in the same raspberry field as the standard yeast sugar water (0.25 oz yeast, 4 tsp sugar, 300 ml water) trap.  As one can instantly see from the chart below, this trap is not as effective as the yeast sugar water trap.  Interestingly, there does seem to be a trend in the yeast sugar water trap depending how close it was placed to a potential source of a lot of spotted wing drosophila, a sensitivity not apparent in the sake trap.

Of interest, however, is the fact that the "sake bomb" was quite effective, much more than the yeast sugar water trap, in drawing in some six other species of flies, including houseflies.  This could be useful information in the case of future infestations of exotic flies.

It was perhaps only inevitable that some laboratory work with a private industry researcher has discovered a high level of tolerance, maybe even resistance, to the popular organically registered pesticide Pyganic  (active ingredient pyrethrin) in spotted wing drosophila.  Using the system of Petri plates photographed below, groups numbering from 15 to 22 flies were subjected to the label rate (18 fl oz) and twice the label rate (36 fl oz) of Pyganic 5.0 II with the result that spraying them had very little effect and most survived.  This has been repeated several times, so we know it is not by chance that this is happening.

The population subjected to this laboratory testing has been exposed in the source field to many applications of Pyganic- there's not a lot of choices in organic culture- over the past two years, so it comes as no surprise.  Admittedly it seems rather fast.  Do note also that pyrethrin is a weaker version of the synthetic pyrethroids such as zeta cyper-methrin (Mustang Max) and bifenthrin (Brigrade) so we do have a flashing yellow with these materials also. 

It is so important that we continue to rotate the pesticides we are using against spotted wing drosophila.

The following is a brief summary of an efficacy trial of several organic materials at different rates and frequencies in a local organically managed raspberry field.

The trial was run as follows:

Treatments were Pyganic 5.0 applied at 9 fl oz per acre, Pyganic 5.0 applied at 18 fl oz per acre, Pyganic 5.0 applied at 18 fl oz per acre + Aza-Direct applied at 2 pt per acre and Entrust applied at 2 oz per acre.

Two applications of all Pyganic materials and mixes were made; one on 6/29 and the other on 7/2.  As per recommendations from the distributor, carrier pH's were modified to below 6.5 with Mix-Well.
Entrust was applied once on 7/2. As per label recommendations, pH was not modified and checked out at 7.0.

Applications made with 75 gal water per acre.

Vacuum evaluations using the bug vac described last November took place before application and last vacuum evaluation was on July 6.  Evaluation of fruit for SWD infestation was made before application and then again on July 7.

Results are encouraging.  Level of fruit infestation as evaluated on July 7 was significantly lower than the untreated control in the 18 oz per acre Pyganic treatments (both alone and mixed with Aza-Direct) and the single application of Entrust.  This trend corresponded strongly with the numbers of flies caught by vacuum up to that date.

It appears that a single application of Entrust or two applications of a high rate of Pyganic can offer organic growers up to five days of SWD control.

There are pesticides mentioned for management of spotted wing drosophila in this article.  Before using any of these products, check with your local Agricultural Commissioner's Office and consult product labels for current status of product registration, restrictions, and use information.